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Abstract
<p class="first" id="d1632650e132">Three-dimensional (3D) porous zinc (Zn) with a
moderate degradation rate is a promising
candidate for biodegradable bone scaffolds. However, fabrication of such scaffolds
with adequate mechanical properties remains a challenge. Moreover, the composition,
crystallography and microstructure of the in vivo degradation products formed at or
near the implant-bone interface are still not precisely known. Here, we have fabricated
porous Fe@Zn scaffolds with skeletons consisting of an inner core layer of Fe and
an outer shell layer of Zn using template-assisted electrodeposition technique, and
systematically evaluated their porous structure, mechanical properties, degradation
mechanism, antibacterial ability and in vitro and in vivo biocompatibility. In situ
site-specific focused ion beam micromilling and transmission electron microscopy were
used to identify the in vivo degradation products at the nanometer scale. The 3D porous
Fe@Zn scaffolds show similar structure and comparable mechanical properties to human
cancellous bone. The degradation rates can be adjusted by varying the layer thickness
of Zn and Fe. The antibacterial rates reach over 95% against S. aureus and almost
100% against E. coli. A threshold of released Zn ion concentration (~ 0.3 mM) was
found to determine the in vitro biocompatibility. Intense new bone formation and ingrowth
were observed despite with a slight inflammatory response. The in vivo degradation
products were identified to be equiaxed nanocrystalline zinc oxide with dispersed
zinc carbonate. This study not only demonstrates the feasibility of porous Fe@Zn for
biodegradable bone implants, but also provides significant insight into the degradation
mechanism of porous Zn in physiological environment.
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